The invention relates to a semiconductor device comprising a semiconductor body having a first region of a first conductivity type and, adjacent thereto, a second region of the second, opposite, conductivity type, a third region of the first conductivity type, which is adjacent the second region and separated from the first region by the second region, and a fourth region of the first conductivity type which is separated from the second region by the third region and which has a higher doping concentration than the third region, the first, the second and the fourth region each being provided with a terminal. Said fourth region may be considered to be a contact zone of the third region of the same conductivity type. Consequently, the succession of various regions described herein forms a horizontal or a vertical npn or pnp structure which can suitably be used, for example, as a transistor (bipolar or MOS) or as a diode.
It has been found that, in practice, such elements often are vulnerable to damage when, during operation, a high voltage is applied in the reverse direction across the pn-junction between the second region and the fourth region while, at the same time, there is a large current flow. This damage may be caused by a local current concentration as a result of a breakdown, leading to a local increase in temperature and causing the field to increase at the junction from region 3 to region 4, which may lead to a further current increase. It is well known that an increase of the breakdown voltage, for example, in the third region can be achieved by providing electrically floating rings or zones of the opposite conductivity type at the edges of the second region, leading to a reduction of the electric field. As the conductivity type of these zones is contrary to that of the third region, the provision of these zones requires an additional process step. Besides, these rings take up comparatively much space, leading to an increase in the size of the circuit element, which may be inconvenient particularly in integrated circuits. It is also possible that this measure results in an increase of the series resistance of the element. A further drawback of this measure resides in that an increase of the electric field strength and current concentration at the junction between the third and the fourth region is suppressed hardly, or not at all.